The invention relates to an exhaust gas turbocharger for an internal combustion engine including an exhaust gas turbine and a compressor driven by the exhaust gas turbine, wherein the turbine comprises a turbine housing with a turbine wheel rotatably supported in the turbine housing.
DE 28 43 202 discloses an exhaust gas turbocharger which includes an exhaust gas turbine driven by the exhaust gases of an internal combustion engine and a compressor, which is coupled to the turbine by a shaft for rotation with the turbine and which compresses inducted combustion air to a charge pressure with which the combustion air is supplied to the cylinder inlets of the internal combustion engine. The housing of the exhaust gas turbocharger consists of three individual housings for the turbine, for the compressor and for the bearing between the turbine and the compressor. Each individual housing is formed as a casting wherein the housing for the turbine and the compressor, which are arranged at opposite sides of the bearing housing, include also the supply and the discharge passages for the turbine and, respectively, the compressor.
The housings, which are manufactured by casting, can be produced inexpensively and they also provide for the necessary safety if the turbine or the compressor wheel should burst. They are however heavy, particularly for utility vehicle applications because they are relatively large, and they require expensive and complicated connecting and support elements for their support in the vehicle. In addition, those high-mass housing have the disadvantage that, because of their high heat capacity, a large amount of heat is stored in the walls of the housings. As a result, a relatively large amount of heat is removed from the exhaust gas supplied to the turbine, whereby the energy supplied to the turbine wheel is reduced which results in power losses particularly after a cold start of the engine.
On the other hand, there is the problem that, after shut down of the engine, the heat stored in the housing, particularly in the area of the turbocharger, may lead to coking of the oil in the charger. The high temperatures may further result in thermal stresses in the housing. In order to avoid excessively high thermal stresses, the housings must be provided with complicated cooling systems whereby the already large weight is further increased.
Another disadvantage resides in the fact that, because of the removal of heat from the exhaust gas, the catalytic converter is insufficiently heated particularly at the beginning of the engine operation so that the catalytic converter becomes fully effective only with a certain time delay.
It is the object of the present invention to provide a turbocharger, which is of a simple design but has a high efficiency. It should also have a relatively low weight.
In an exhaust gas turbocharger for an internal combustion engine including an exhaust gas turbine and a compressor connected to the turbine so as to be operated thereby, the turbine includes a housing consisting of an inner and an outer shell formed from steel sheets arranged in spaced relationship so as to form therebetween an intermediate.
A coolant may be conducted through the space between the sheet metal shells. The two metal shells, which delimit particularly a spiral passage for guiding the exhaust gas to the turbine wheel, arexe2x80x94compared with the cast components of the state of the artxe2x80x94relatively lightweight since the relatively thin sheet metal walls are substantially lighter than the cast walls. Inspite of the small wall thickness, they have a high burst resistance. Another advantage is the low heat storage capacity of the double wall of sheet metal whereby the thermal efficiency of the turbocharger and also the start-up behavior of the catalytic converter of the respective engine are improved. There is no need for providing the heat shield panels by means of which the radiation heat has been contained in the past.
In a particular embodiment, the inner and outer sheet metal shells consist of sheet steel wherein the outer sheet consists of temperature resistant material and the inner sheet consists of a high-temperature resistant material. The inner metal shell is in direct contact with the hot exhaust gas and is therefore heated to a greater degree than the outer metal shell, which is not contacted by the hot exhaust gas. The inner shell, which delimits the spiral inlet passage and which consists of a highly temperature resistant material is selected so that it is resistant to the high exhaust gas temperatures. The outer shell, which extends around the inner shell, however is not in contact with the exhaust gas so that it can be made of a material with lower temperature resistance than that of which the inner shell is made.
The inner shell as well as the outer shell can be shaped parts formed by suitable deformation techniques, such as internal high-pressure shaping procedures, from planar metal sheets. They may have complex shapes to form for example the spiral gas inlet channel of the turbine. It is also possible to form a spiral inlet with two inlet passages from a single inner shell, the two passages of the spiral channel being separated by a divider wall, which is formed by an appropriate shaping of the inner shell.
The inner and the outer shells are preferably constructed so as to be separated from the exhaust channel of the turbine wherein the turbine wheel is supported. The exhaust channel which, at the opposite side of the turbine wheel, may be connected with a bearing housing is preferably a casting which is capable of withstanding the static and dynamic forces of the turbine wheel and which is capable of maintaining its original shape and dimensions. The inner and the outer shells are separate from the outlet channel and are therefore not subjected to the high forces effective on the turbine wheel. The heat generated by the turbine wheel is generally taken up and conducted out by way by the exhaust channel so that the inner and outer shell remain to a large degree unaffected by the heat generated by the turbine wheel.
The intermediate space between the inner and the outer shells may accommodate a coolant, which, in a preferred embodiment, is admitted by way of inlet nozzles and discharged by way of outlet nozzles. In another embodiment, the turbine housing, which consists of inner and outer shells, may form a single component with an exhaust manifold, which is mounted to the cylinder outlet of the internal combustion engine.
The invention will become more readily apparent from the following description of particular embodiments thereof on the basis of the accompanying drawings.